There are a variety of adhesives for composites such as particle boards, fiber boards, and textile composites. Generally these adhesives are made from urea resins, urea-melamine resins, phenolic resins, and the like. In order to impart sufficient water-resistant properties to the constructions made with these resins, attempts have been made to combine a wax emulsion sizing agent with the resin. However, it has been very problematic to obtain a stable blend of resin and wax emulsion. Wax solids may not remain homogeneously suspended in mixtures with water-borne resins, particularly during transport, transfer, and use. Thus, the resin-wax blend needs to be used immediately or else separation occurs resulting in non-uniformity in the water-repellency and bond quality imparted to the composite by the adhesive. Further, since wood shrinks and swells as its moisture content varies, if the composite is not properly treated with a sizing agent and resin, the composite will have less integrity or debond on exposure to moisture.
Often the wax emulsion is combined with the resin at the time of use. Of course this complicates handling and mixing at the site of use. It would be much more convenient to provide the user with a ready-to-use adhesive that requires no mixing prior to application.
U.S. Pat. No. 4,407,999 attempts to provide a single component, ready-to-use (RTU), water repellant adhesive composition for wooden material, purportedly having good blendability and storage stability. The adhesive consists essentially of a paraffin emulsion containing oxidized paraffin and a resin such as a phenolic resole resin. This patent suggests that by using an oxidized paraffin having an acid value of from 10 to 70 and a melting point of from 30 to 90.degree. C., with the conventional paraffin wax component, one can successfully prepare a pre-blended adhesive from the resin and wax emulsion. Too low an acid value makes emulsification of the wax difficult; too high a value reduces the water resistance of the composite. The wax emulsion is prepared in the presence of a surfactant and/or a water-soluble alkali metal compound such as sodium hydroxide. Blending of wax emulsion and resin is carried out from ambient temperature to 60.degree. C.